The Proteomics Facility Core provides analytical proteomics services to investigators in the P30 EHS Core Center Analytical proteomics integrates tools for protein and peptide separations, mass spectrometry (MS) analysis, and bioinformatics to characterize proteomes and their component proteins {1-3). Proteomics is the study of proteins and proteomes, the functional complements to genomes which comprise diverse structural and functional multiprotein machines (3). Proteomics approaches offer new tools for the molecular analysis of biological systems, the identification of therapeutic targets and mechanisms, and the identification of markers for disease and therapeutic response. In the context of this P30 EHS Core Center, the Proteomics Facility Core provides essential support for the characterization of chemical modification of proteins, including protein adducts derived from xenobiotics and reactive intermediates generated in situ, as well as regulatory post-translational modifications (4). The Proteomics Facility Core also provides essential support for the identification of interacting partners of proteins in multiprotein complexes, as well as analyses of complex proteomes and subproteomes. Research Interactions The Proteomics Core also provides a research technology platform for more elaborate, challenging, and advanced studies that require customized experimental designs, analytical approaches, and expertise. These research functions of the core are defined as those analytical tasks that fall outside the usual scope of the fee-for-service functions and require the sustained interaction of a Center Investigator's laboratory with a Proteomics Associate Director and skilled staff supported by the Proteomics Facility Core component of the Center grant. Because the following research services may involve an open-ended commitment of time by Core faculty, professional effort will be recorded and traced to individual projects so that no single investigator places an undue burden on the professional staff in excess of the support provided by the P30 EHS Core Center For examples of past research interactions of Center Investigators in the Proteomics Facility Core, see the Progress Report section, pp. 304-311.